1. Field of the Invention
The present invention relates to an electric device for detecting the level of milk in a receptacle installed in a milking system for accumulating milk drawn from at least one animal. The device of the invention is designed to reduce as much as possible the production of stray current susceptible to affect the animal being milked.
2. Brief description of the prior art
The milking of cows has become over the years highly automated. In the present vacuum milking systems, milk pipes continuously carry the milk drawn from the cows being milked toward a milk storage tank. Creation of an adequate vacuum in the milk storage tank to draw the milk thereto is problematic as the storage tank is large and cannot be adequately sealed because of the various stirring and cooling equipments connected thereto.
To solve this problem, a smaller milk jar is installed in the milking system between the milk-conveying pipes and the storage tank. A vacuum is created in this jar to draw the milk therein. When the milk accumulated in the jar reaches a given level, a pump is activated to transfer milk from the jar to the storage tank.
To detect the level of milk, electrodes are mounted in the jar at predetermined levels. A controller monitors the level of milk through the electrodes to activate the pump and transfer the milk from the jar to the storage tank.
The operation of the prior art pump controllers is simple. It consists of establishing an AC current having a frequency of 60 Hz through the milk when two electrodes are interconnected by the milk, to thereby indicate that the milk has reached a predetermined level in the jar. This current energizes the coil of a relay to close its normally open contacts and activate the pump to transfer the milk from the jar to the storage tank.
To establish the current through the milk, the prior art controllers apply to one of the electrodes a voltage of 60 Hz of sufficient amplitude to create a stray current affecting the cows being milked. As milk is a very good electric conductor because of the large quantity of fat particles it contains, the electrode voltage establish a stray current from the electrode, the milk in the jar, milk residue on the inner surface of the milk pipes, the teat cup clusters, the cow and the ground. This is a major drawback since animals, including cows are very sensitive to 60 Hz currents flowing through their body. Behavior anomalies such as nervousness and restlessness have been not:iced on cows subjected to 60 Hz currents as low as 1 mA. Since these currents flow through the teats and udder of the cows, they cause problems such as milk retention, whitened teats, sphincter problems, rise in the quantity of somatic cell count. Of course, diminution of production can arise from these stray currents.